1. Field of the Invention
The present invention relates to a power output apparatus and a hybrid vehicle with a power output apparatus mounted thereon. More specifically the invention pertains to a power output apparatus that outputs power to a drive shaft, as well as to a hybrid vehicle with such a power output apparatus mounted thereon.
2. Description of the Prior Art
Various power output apparatuses mounted on a hybrid vehicle have been proposed, where an output shaft of an internal combustion engine and rotating shafts of two motors are connected with respective shafts of a planetary gear (for example, JAPANESE PATENT LAID-OPEN GAZETTE No. 9-56009). The power output apparatus has an oil pump that feeds a supply of lubricating oil to mechanical part including the planetary gear and is attached to the output shaft of the internal combustion engine or a drive shaft.
In a hybrid vehicle with the power output apparatus including the oil pump attached to the output shaft of the internal combustion engine, however, a sufficient supply of lubricating oil to the planetary gear is not assured in an EV drive mode, where the hybrid vehicle runs with the power from the motor, while the internal combustion engine is at a stop. In a hybrid vehicle with the power output apparatus including the oil pump attached to the drive shaft, on the other hand, a sufficient supply of lubricating oil to the planetary gear is not ensured in a stop-time charging mode, where a battery mounted on the hybrid vehicle is charged with power from the internal combustion engine, while the vehicle is at a stop.
One possible measure against this problem attaches separate oil pumps to the output shaft of the internal combustion engine and to the drive shaft. Attachment of the multiple oil pumps, however, undesirably increases the number of components included in the vehicle and raises the total weight of the vehicle. Another possible measure uses an electrically-driven oil pump that does not gain the power from the output shaft of the internal combustion engine or the drive shaft. This electrically-driven oil pump converts the power output from the internal combustion engine into electric power and actuates with the converted electric power. The electrically-driven oil pump thus lowers the overall energy efficiency of the vehicle, compared with the oil pump that actuates with the power from the output shaft of the internal combustion engine.